The present invention relates, in general, to an apparatus for detecting a diaphragm failure, and, more specifically, to an apparatus for detecting a failure of a semiconductor diaphragm.
With recent advances in micro-machining technology, semiconductor diaphragms are finding their way into various applications. For example, semiconductor diaphragms are used in semiconductor pressure sensors, flow sensors, acceleration sensors, micro-machining relays, and actuators that control inflow and outflow of fluids, and so forth. Although an apparatus of this type that uses a semiconductor diaphragm may be utilized in a variety of industrial applications, its potential benefit in the field of medical equipment is also anticipated, because a kind of very small pump structure may be fabricated in a miniature area measuring only several millimeters square.
FIG. 1A is a cross-sectional view of a prior art piezoresistive-type pressure sensor (10) that uses a semiconductor diaphragm. FIG. 1B is a plan view of the pressure sensor (10), where a cross section along Axe2x80x94A is represented by FIG. 1A. The pressure sensor (10) is comprised of a diaphragm (13), an N-type semiconductor substrate (11) that supports the diaphragm, and a piezoresistive element (12) formed of a P- diffusion layer disposed on the diaphragm (13), wherein for the piezoresistive element, a predetermined electrical wiring pattern is made to a power supply and a pressure sense terminal (not shown).
The pressure sensor (10) operates as follows. First, when no external pressure is applied, no stress acts upon the piezoresistive elements (12-1) through (12-4), so that an electrical signal derived from the pressure sense terminal indicates that no pressure is applied. Next, when an external pressure is applied, the diaphragm (13) deflects in the direction of arrow (14). This deflection causes the piezoresistive elements (12-1) through (12-4) to be stressed in the direction of arrow (15) or (16). Different directions of stress acting upon each piezoresistive element are attributable to the locations of the piezoresistive elements. That is, the piezoresistive elements (12-1) and (12-3) are disposed normal to the peripheral portion of the diaphragm, whereas the piezoresistive elements (12-2) and (12-4) are located in parallel. It should be appreciated that each piezoresistive element is located around the diaphragm because the stress, which is developed around the diaphragm when it is deflected, is greater than that developed in other portions. Depending upon the stress acting in the direction of arrow (15) or (16), the resistance of the piezoresistive elements (12-1) and (12-3) increases or decreases, while the resistance of the piezoresistive elements (12-2) and (12-4) decreases or increases. As a result, the pressure can be sensed by detecting the potential difference developed on the pressure sense terminal.
With such a prior art diaphragm-based apparatus, there is no mechanism for detecting any failure, when failures, such as fracture, cracking, deformation, and damage, are developed in the diaphragm. The present invention has its objective to provide an apparatus that can facilitate simple detection of diaphragm failures.
Furthermore, when a semiconductor diaphragm-based apparatus is fabricated, any failure that occurs during the wafer fabrication process cannot be detected at a wafer level (or wafer process). Failures cannot be detected until the assembly of the entire apparatus is completed after the wafer fabrication process. With a semiconductor pressure sensor, for example, it is determined whether the diaphragm is acceptable or not, only after the pressure sensor is assembled and tests are conducted for its output characteristics by applying external pressure thereto. Accordingly, it is an objective of the present invention to provide an apparatus that can facilitate simple detection of diaphragm failures at a wafer level.
Diaphragm failures may occur not only during the fabrication process, but also while it is used by the user. During its use by the user, it is generally difficult to determine whether any failure has occurred in the diaphragm. For example, it is hard to determine whether the output data derived from the semiconductor pressure sensor is normal as external pressure is applied thereto or it reflects any diaphragm failure. Accordingly, the present invention has its aim to provide an apparatus that can facilitate simple detection of diaphragm failures even during its use by the user.
Furthermore, a small damage on the diaphragm, at first, may gradually grow later. Accordingly, it is another objective of the present invention to provide an apparatus that permits early detection of diaphragm failures.
The above objectives are achieved by an apparatus for detecting a diaphragm failure, comprising: a diaphragm; a substrate for supporting the diaphragm; and a line-shaped resistor disposed in at least one side of the diaphragm. One end of the line-shaped resistor is coupled to a failure detection terminal. In one embodiment, the line-shaped resistor is formed around and at a center of the diaphragm, and the line-shaped resistor is comprised of multiple line elements, so that distances from one line element to its adjacent line elements are substantially equal. Also, layout patterns of at least two line elements are similar in figure to each other.
The failure detection apparatus according to the present invention has a line-shaped resistor formed on a diaphragm, with one end of the line-shaped resistor coupled to a failure detection terminal. When any diaphragm failure occurs, the resistance value of the overall line-shaped resistor differs from that under a normal condition. The failure detection terminal is used to measure the resistance value of the line-shaped resistor, which is compared against a normal value, thereby allowing for detection of a diaphragm failure.